Replies

1. 
   Mike_Maines_ | Dec 10, 2001 06:41am | #1

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   Brent, I have always installed bird blocks in plane with the face of the wall. If you're installing them perpendicular to the roof surface, a little trig would get you the for formula. I think it would be quicker and easier to use a straightedge and a speed square to get the bevel angle, and use your layout lines to get the short and long points for the miter angle.

1. 
   Ken_Drake | Dec 10, 2001 01:58pm | #2

   *Brent,To find the "face angle" on the bird block, use the UNIT RISE on the tongue of a framing square with the UNIT RAFTER LENGTH on the body. (For newbies,The UNIT RAFTER LENGTH is the length of a rafter for 12" of run) Mark the tongue for the angle of the cut.Example: 9/12 pitch roof. UNIT RISE = 9, UNIT RAFTER LENGTH = 15. Use 9 on tongue and 15 on body and mark the tongue for the angle of the cut.Follow these steps to get the circular saw bevel:1) square the unit rise, then double your answer.9²=81, 2x81=1622) add 144 to result of step 1162 + 144 = 3063) find the square root of step 2square root(306)=17 1/2 (rounded)Now, use 12 on the tongue of the framing square with 17 1/2 on the body, and mark the tongue. Use a speed square to measure the angle that you marked. That's the circular saw bevel. In this case, 34 1/2º.The above information is applicable for single pitch hip roofs at 90º corners only.Ken

1. 
   Joseph_Fusco | Dec 11, 2001 12:01am | #3

   *Brent,

   Or you can just work with the numbers you have. If you have a 9/12 roof you can get the unit length of the square (first number under 9 on the body) then it's just a matter of sqrt(92 + 152) = 17.5 Tan-1 (12/17.5) = 34.45° It's even simpler just to use the square for the entire operation and leave the math home. . .

   View Image"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle

1. 
   MassDriver | Dec 17, 2001 08:17am | #4

   *Thanks guys. That's exactly what I needed.Brent Jackson.

2. 
   Wedertz | Jul 28, 2021 04:02am | #6

   Im definitely going to try this. I’m curious why do you add the 144?

2. 
   MassDriver | Dec 17, 2001 08:17am | #5

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   When cutting that last block against the Hip or Valley rafter, does anyone know the Non-trial-and-error method for finding the correct compound angle for matching the rafter. It has been so long since I've had to cut one I just cannot remember. This is the block that sits at a perpendicular angle to the pitch of the roof for "bird blocks".
   Brent Jackson.